Netgear router does not detect internet from modem

My new Netgear WGR614v7 does not detect the internet from my modem, an Alvarion ACPS-101G Rev C (Power IDU PS1065).

My internet connection is working because I can connect using PPPoE via an ethernet cable from the modem direct to my computer (iMac). The internet connection uses WiMAX and established via a wi-fi receiver/transmitter on the roof of my house.

The Netgear router's ''internet'' light flickers orange to indicate it is looking for a connection but it doesn't turn green. I had a brief period of about 10 mins when I first unpacked and connected up the router but after a few minutes the connection dropped and the orange light came back. I haven't managed to get a connection since.

A guy in one computer shop told me that it's important that the router is the correct Annex (Annex B in this case) but tech support at my ISP said my Netgear router should work fine with either A or B.

So, why does my router not detect the internet?
Thanks